Dental restorative composites containing 2,2-bis-[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane derivatives and spiro orthocarbonates

Various dental restorative composite resins containing 2,2-bis-[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA) derivatives and spiro orthocarbonates (SOCs) were explored for minimizing the volumetric shrinkage that generally occurs during polymerization. Previous reports suggested mixing Bis-GMA with its derivative TMBis-GMA (2,2-bis[3,5-dimethyl-4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane) to obtain a dental composite with low volumetric shrinkage. It was hypothesized that spiro orthocarbonates would expand volumetrically during polymerization, because of their sophisticated ring-opening reactions; therefore several of them were added to the mixture of Bis-GMA and TMBis-GMA to bring about further reductions in volumetric shrinkage. It was indeed possible to reduce the extent of volumetric shrinkage of dental composites containing SOCs, and to do so without compromising these resins' mechanical properties.     

Preparation of low shrinkage stress Bis-GMA free dental resin composites with a synthesized urethane dimethacrylate monomer

A new urethane dimethacrylate TMA was synthesized through a typical urethane reaction. TMA was used to replace 1,6-bis(methacryloxy-2-ethoxycarbonyl- amino)-2,4,4- trimethylhexane (UDMA) in UDMA based composite partially or totally to prepare TMA containing composites. Critical properties of TMA containing composites were investigated. 2,2-bis[4(2-hydroxy-3-methacryloy- propyloy)phenyl]propane (Bis-GMA) based and UDMA based composites were used as references. FT-IR and ¹H-NMR confirmed the structure of TMA. All of experimental dental resin composites had the similar double bond conversion (p?>?0.05). With a certain amount of TMA, TMA containing composites could have lower volumetric shrinkage (p?<?0.05) and shrinkage stress (p?<?0.05) than control groups. Water sorption, solubility, flexural strength and modulus of TMA containing composites were not worse than those of control groups. All of TMA containing composites and UDMA based composite had the same fracture toughness (p?>?0.05), which was higher than that of Bis-GMA based composite (p?<?0.05). TMA has potential as Bis-GMA substitute to prepare Bis-GMA free dental resin composites with low shrinkage stress.     

Low viscosity dimethacrylate comonomer compositions [Bis-GMA and CH3Bis-GMA] for novel dental composites; analysis of the network by stray-field MRI,solid-state NMR and DSC & FTIR

The effect of dilution of 2,2-bis (4-(2-hydroxy-3-methacryloxyprop-1-oxy) phenyl) propane (Bis-GMA) with 2,2-bis(4-(2-methacryloxyprop-1-oxy)phenyl) propane (CH3Bis-GMA) on extent of polymerization (Ep) was investigated by FTIR and NMR. The results correlate well with Ep values of the system and its flexibility probed by Tg (obtained by DSC). Spatially resolved photopolymerization kinetics and polymerization shrinkage (PS, i.e. volumetric polymerization contraction) was also studied by stray-field imaging (STRAFI-MRI). PS was obtained in the presence of oxygen from the atmosphere as the total volumetric contraction. All the results were compared with those obtained for the Bis-GMA/TEGDMA (triethylene glycol dimethacrylate) system. Use of Bis-GMA mixed with hydrophobic low viscosity CH3Bis-GMA comonomer, as a substitute for the commonly used TEGDMA, resulted in improving significantly properties such as PS, water sorption and Ep, thereby reducing the unreacted double bond concentration.     

Synthesis and characterization of new dimethacrylate monomer and its application in dental resin

In this study, a dimethacrylate monomer, 1,4-Bis[2-(4-(2′-hydroxy-3′-methacryloyloxy-propoxy)phenyl)-2propyl]benzene (BMPPB) was synthesized to replace 2,2-bis[4-(2′-hydroxyl-3′-methacryloyloxy-propoxy)phenyl]propane (Bis-GMA) as one component of dental restorative materials. The structure of BMPPB and its intermediate product 1,4-bis[2-(4-(oxiranylmethoxy)phenyl)-2propyl]benzene (BOPPB) were confirmed by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance spectroscopy (¹H-NMR), and elemental analysis. In order to evaluate the possibility of replacing Bis-GMA with BMPPB in dental resin, double bond conversion (DC), polymerization shrinkage, contact angle, water sorption (WS) and solubility (SL), and flexural strength (FS) and modulus of BMPPB/tri(ethylene glycol)dimethacrylate (TEGDMA) (50/50?wt) resin system and Bis-GMA/BMPPB/TEGDMA (25/25/50?wt) resin system were studied. Commercially used Bis-GMA/TEGDMA (50/50?wt) dental resin system was used as reference. The results showed that BMPPB-contained copolymer had higher DC, higher WS and SL than the copolymer that only contained Bis-GMA (p?<?0.05). All of the copolymers had nearly the same contact angle (p?>?0.05). BMPPB/TEGDMA resin system had lower polymerization shrinkage, higher FS and modulus (p?<?0.05) than Bis-GMA/TEGDMA resin system. There was no significant difference on polymerization shrinkage, FS and modulus (p?>?0.05) between Bis-GMA/BMPPB/TEGDMA resin system and Bis-GMA/TEGDMA resin system. Before and after water immersion, both FS and modulus of every copolymer did not change significantly (p?>?0.05). Therefore, BMPPB had potential to be used to replace Bis-GMA as base resin in dental restorative materials, but many studies should be undertaken further.     

Adhesive layer properties as a determinant of dentin bond strength

The goal of this study is to evaluate the hypothesis that the properties of the resin adhesive might affect the microtensile bond strength (MTBS) of multibottle dental adhesive system. In order to alter the properties, the experimental resin adhesives containing 2,2-bis (4-2-hydroxy-3-methacryloyloxypropoxyphenyl)propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) at various ratios were prepared. Degree of conversion immediately after curing (DC-immed), degree of conversion at 48 h after curing (DC-48h) of a thin coat of the experimental adhesives, the flexural strength (FS) of the bulk specimens made of the experimental adhesives, pH, viscosity at shear rate of 1 S(-1), and the microtensile bond strength (MTBS) values of the adhesives to dentin were investigated. The maximum MTBS and FS values of the resin adhesives were observed when the ratio of Bis-GMA/TEGDMA was 60/40. However, pH and viscosity values increased with increasing Bis-GMA content in the adhesives. When Bis-GMA content was more than 60 wt %, the viscosity increased exponentially and restricted the DC and FS, and accordingly decreased the bond strength. The stronger the resin adhesives were, the higher the bond strength to dentin could be obtained.     

Development of highly reactive mono-(meth)acrylates as reactive diluents for dimethacrylate-based dental resin systems

Reactive diluents such as triethyleneglycol-dimethacrylate (TEGDMA) have been widely used with bisphenol-A-glycidyl-dimethacrylate (Bis-GMA) to achieve restorative resins with appropriate viscosity and higher conversion. However, additional water sorption and polymerization shrinkage were also introduced. The aim of this work is to investigate whether the cure and material properties can be improved in dental resins containing novel mono-(meth)acrylates as reactive diluents so that these Bis-GMA-based copolymers have reduced polymerization shrinkage but higher overall double bond conversion. Several ultra-high-reactivity mono-(meth)acrylates that contain secondary functionalities have been synthesized and investigated. The polymerization rate and double bond conversion were monitored using photo-FTIR. Polymerization shrinkage, dynamic mechanical analysis, and flexural strength were characterized. Compared with the Bis-GMA/TEGDMA control, the Bis-GMA/mono-methacrylate systems studied showed higher final conversions, faster curing rates, and decreased polymerization shrinkage. Our optimum system Bis-GMA/morpholine carbamate methacrylate achieved 86% final conversion (vs. 65%), a polymerization rate 3.5 times faster, and a 30% reduction in polymerization volumetric shrinkage. These results indicate that certain highly reactive, novel mono-(meth)acrylates possess very promising potential to replace TEGDMA as reactive diluents and can readily be applied to develop superior dental resins.     

Synthesis and photopolymerization of N,N'-dimethyl,-N,N'-di(methacryloxy ethyl)-1,6-hexanediamine as a polymerizable amine coinitiator for dental restorations.

N,N'-dimethyl,-N,N'-di(methacryloxy ethyl)-1,6-hexanediamine (NDMH) was synthesized for the purpose of replacing both triethylene glycol dimethacrylate (TEGDMA) and the non-polymerizable amine which is added as a coinitiator in dental resin mixtures, 2,2-bis[4(2-hydroxy-3-methacryloxypropoxy)phenyl] propane (bis-GMA), camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (EDAB) were used as monomer, photoinitiator and coinitiator, respectively, in these model dental resin systems. Mixtures of bis-GMA/TEGDMA/CQ/EDAB and bis-GMA/TEGDMA/CQ/NDMH were found to reach final conversions of about 45%, slightly higher than his-GMA/NDMH/CQ (40%) under comparable visible light irradiation conditions. In addition, samples cured to these conversions were tested with dynamic mechanical analysis. The bis-GMA/TEGDMA/CQ/EDAB, his-GMA/TEGDMA/CQ/NDMH and bis-GMA/NDMH/CQ mixtures were found to have approximately the same glass transition temperature and modulus. Finally, the water sorption and solubility of bis-GMA/NDMH/CQ were higher than those of the bis-GMA/TEGDMA/CQ/EDAB, and bis-GMA/TEGDMA/CQ/NDMH. However, the values were still within the range of the ISO 9000's standards. These results suggest that NDMH is a viable alternative to conventional photocuring dental resins, serving both as a diluent and coinitiator, since there are no large differences in physical and mechanical properties when using NDMH to replace the amine coinitiator and TEGDMA diluent. The key advantage to this system is that the dimethacrylate NDMH can copolymerize with bis-GMA and TEGDMA, limiting the amount of extractable amine.     

Investigation of double bond conversion,mechanical properties,and antibacterial activity of dental resins with different alkyl chain length quaternary ammonium methacrylate monomers (QAM)

In order to endow dental resin with antibacterial activity, a series of antibacterial quaternary ammonium methacrylate monomers (QAM) with different substituted alkyl chain length (from 10 to 18) were incorporated into commonly used 2,2-bis[4-(2′-hydroxy-3′-methacryloyloxy-propoxy)-phenyl]propane (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) (50?wt/50?wt) dental resin as immobilized antibacterial agents. Double bond conversion (DC), flexural strength (FS) and modulus (FM), and young and mature biofilms inhibition effectiveness of prepared dental resins were studied and Bis-GMA/TEGDMA without QAM was used as reference. Results showed that there was no significant difference on DC, FS, and FM between copolymer with and without 5?wt% QAM. Substituted alkyl chain length of QAM had no influence on DC, FS, and FM of copolymer, but had influence on antibacterial activity of copolymer. Antibacterial activity of copolymer increased with increasing of substituted alkyl chain length of QAM, and the sequence followed as 5%C10?<?5%C11≈5%C12?<?5%C16≈5%C18. Copolymers containing C18 and C16 had the best inhibition effectiveness on both young biofilm and mature biofilm, copolymers containing C12 and C11 only had inhibition effectiveness on young biofilm and copolymer containing C10 had none inhibition effectiveness on neither young biofilm nor mature biofilm.     

Mechanical and antibacterial properties of benzothiazole-based dental resin materials

A synthesized benzothiazole containing mono-methacrylate monomer BTTMA was incorporated into Bis-GMA/TEGDMA dental resin system with a series of mass concentration from 5 to 30 wt.% as an antibacterial agent. The influence of BTTMA on physicochemical properties of dental resin system, such as double bond conversion (DC), volumetric shrinkage (VS), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL) were investigated. Direct contact testing and agar diffusion testing were used to evaluate the antibacterial activity of BTTMA containing dental resin. The results showed that BTTMA could endow dental resin with significant antibacterial activity when its concentration reached a certain amount (20 wt.%), and the antibacterial activity of BTTMA containing dental resin was mainly attributed to the immobilized BTTMA instead of the unreacted leachable BTTMA. BTTMA had no negative effect on physicochemical properties of dental resin, and even some BTTMA containing dental resins had advantages like higher DC, lower VS and WS when compared with control resin. Therefore, BTTMA could be considered as a suitable antibacterial agent in dental material, but much more researches concerned about biocompatibility should be done in future to prove whether it could be applied in clinic.     

A new method for quantifying the intensity of the C=C band of dimethacrylate dental monomers in their FTIR and Raman spectra

The degree of conversion (DC) of methacrylate dental resins is typically determined by spectroscopically measuring the decrease of the vinyl (C=C) stretching band at 1640 cm(-1), ratioed before and after polymerization to an internal standard (aromatic ring quadrant stretching vibration (Ph)) at around 1609 cm(-1). While standard methods exist for measuring the intensity of the C=C and Ph peaks from the FTIR or Raman spectrum, these methods either fail under certain circumstances, or lack a physical basis, being purely based on spectral features. In this study, we present a rigorous method (named rotational isomerism method) for determining the intensity of the vinyl and aromatic bands from the FTIR and Raman spectra of dental monomer mixtures, and compare it to a standard baseline method (SBM) and a standard curve fitting method. Model triethyleneglycol dimethacrylate (TEGDMA)/2,2-bis(4-hydroxyphenyl)propane (Bisphenol-A) and TEGDMA/2,2-bis(4-(2-hydroxy-3-methacryloxypropoxy)phenyl)propane (Bis-GMA) mixtures with a series of known C=C/Ph molar ratios were prepared in order to simulate the effect of curing. The accuracy of the new method for measuring the DC was found to be as good as the commonly used SBM. The standard curve fitting method was shown to be inappropriate for measuring C=C/Ph ratios by FTIR spectroscopy due to its inability to realistically simulate the features of the spectra. The insight gained through the use of this new method may be useful for the characterization of other methacrylate biomaterials.     

Properties of acrylic bone cements formulated with Bis-GMA

Experimental cement formulations were prepared by replacing part of the methylmethacrylate (MMA) liquid phase of a conventional surgical cement with an equivalent weight of 2,2-bis [4(2-hydroxy-3-methacryloxypropoxy) phenyl] propane (Bis-GMA), which is the reaction product of diglycidyl ether of bisphenol A and methacrylic acid. It was found that up to 50 wt % of the MMA could be replaced by Bis-GMA without reductions in flow characteristics of the precured polymers. Cements containing 20, 30, 40, and 50 wt % of Bis-GMA in the liquid component were prepared. Over this range of Bis-GMA wt %, it was found that, relative to the unmodified cement, the volumetric shrinkage (DV), the peak temperature reached during the polymerization reaction (Tp), and the flexural strength (obtained in three-point bend tests) were each significantly reduced, the flexural modulus (obtained in three-point bend tests) increased significantly, the compressive strength increased slightly, while there were no significant effects on any of the other properties determined, namely, degree of conversion of the monomer during the polymerization reaction and the glass transition temperature. The drops in D(V) and Tp indicate that cements whose liquid monomers are modified using Bis-GMA hold promise for use in anchoring total joint replacements. The increase in the crosslinking density with increasing amount of Bis-GMA renders the polymer matrix more brittle. This feature was considered responsible for the reduced flexural strength.     

Reinforcement of polymers of 2,2 bis-4(2-hydroxy-3-methacryloyloxy propoxy) phenyl propane by ultra-high modulus polyethylene fibres.

A study has been made of the reinforcement of 2,2 bis-4(2 hydroxy-3-methacryloyloxy propoxy) phenyl propane/tetra-hydrofurfuryl methacrylate copolymers with ultra-high modulus polyethylene fibres. The fibres were orientated longitudinally, in loadings up to 50% w/w, and both untreated and surface treated fibres were studied. Modulii up to approximately 35 GPa were achieved in the axial direction, and the specimens could not be broken in the simple flexure test employed. Electron microscopy of fractured specimens showed extremely good contact between resin and fibre. No deterioration in properties was observed over 6 months in water.     

Trifunctional methacrylate monomers and their photocured composites with reduced curing shrinkage,water sorption,and water solubility

Novel trifunctional methacrylates, 1,1,1-tris[4-(2'-acetoxy-3'-methacryloyloxypropoxy)phenyl]ethane (Ac-THMPE) and 1,1,1-tris[4-(2'-acetoxy-3'-methacryloyloxypropoxy)phenyl]methane (Ac-THMPM), have been prepared by acetylation of the hydrophilic hydroxyl groups of 1,1,1-tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]ethane (THMPE) and 1,1,1-tris[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]methane (THMPM), respectively, for use as dental monomers. Decrease in monomer viscosity resulted from the acetylation. Unfilled resins and composites based on the four trimethacrylates were evaluated for photopolymerization conversion, water contact angle, and curing shrinkage. Water sorption, water solubility, and flexural strength of the composites prepared from the trimethacrylate were measured. Those data obtained for the trimethacrylate-containing materials were compared with control 2,2-bis[4-(2'-hydroxy-3'-methacryloyloxypropoxy)phenyl]propane (bis-GMA)-based materials in order to evaluate the applicability of the trimethacrylates as dental monomers. The acetylation of hydroxyl groups appeared to be an effective method to decrease curing shrinkage, water sorption, and water solubility of the dental composites. When compared with the bis-GMA composite, the composites based on Ac-THMPM and Ac-THMPM showed much lower curing shrinkage, water sorption, and water solubility, along with approximately equal conversion and flexural strength.     

Synthesis,Characterization and Photopolymerization of a New Dimethacrylate Monomer Based on (α-Methyl-benzylidene)bisphenol Used as Root Canal Sealer

Methacrylate resin-based sealers have attracted wide attention because of their easy handling, superior aesthetic qualities, good mechanical properties and excellent adhesive ability with dentin. 2,2-Bis[4-(2′-hydroxy-3′-methacryloyloxypropoxy)-phenyl]-propane (Bis-GMA) is the main component of the newly developed commercial root canal sealer 'Epiphany', which is one of the methacrylate resin-based sealers. In order to further reduce the polymerization volume shrinkage of Bis-GMA, 4,4′-(α-methylbenzylidene)-bis(2′-hydroxy-3′-methacryloyloxy-propoxy)benzene (4,4′-AMBHMB) with higher molecular weight and larger molecular volume was synthesized to replace Bis-GMA as one of the components of the root canal sealer used in this study. The structure of monomer 4,4′-AMBHMB was confirmed by FT-IR, ¹H-NMR, mass spectrum and elemental analysis. The photopolymerization behavior of mixture of 4,4′-AMBHMB and triethylene glycol dimethacrylate (TEGDMA) was investigated by FT-IR. Degree of double bond conversion, volume shrinkage, water sorption and solubility, diffusion coefficient value, flexure strength and glass transition temperature of 4,4′-AMBHMB/TEGDMA system with a mass ratio of 50:50 were measured. A 50:50 Bis-GMA/TEGDMA formulation was used as reference. The results illustrated that 4,4′-AMBHMB/TEGDMA system had the same double bond conversion and water sorption with Bis-GMA/TEGDMA system. Polymerization shrinkage, water solubility and diffusion coefficient of 4,4′-AMBHMB/TEGDMA system were lower than that of the Bis-GMA/TEGDMA system, whereas the flexural strength and glass-transition temperature of 4,4′-AMBHMB/TEGDMA system were higher than that of the Bis-GMA/TEGDMA system.     

HPLC analysis of eluted monomers from two composite resins cured with LED and halogen curing lights

This study investigated the leaching of monomers (Bis-GMA and TEGDMA) from nano-hybrid (Filtek Supreme) and flowable (Filtek Flow) dental composite resins cured with LED or conventional halogen curing lights, and immersed in saliva or water for 24 h. Nine disc specimens were made for each experimental group. After the polymerization process, the specimens were immersed in either water or saliva and incubated at 37 degrees C for 24 h. Eluted Bis-GMA and TEGDMA monomers were detected using high performance liquid chromatography (HPLC). The data were analyzed using three-way ANOVA (p = 0.05) and the independent samples t test. TEGDMA (53.15-1 microg/L) was leached from the resins at a higher level than Bis-GMA (28-0.5 microg/L) (p < 0.01), regardless of the affecting factors: composite type, solvent (media) and type of curing light. In general, Filtek Flow resin released more TEGDMA than Filtek Supreme (p < 0.05), but the Supreme resin released more Bis-GMA than TEGDMA (p < 0.05). Halogen light induced greater monomer elution than LED light immersion in water. Saliva released more TEGDMA than water (p < 0.05). We conclude that (1) total leached TEGDMA was higher than total Bis-GMA, (2) saliva and halogen light (lower intensity than LED) leached more monomers from the resins, and (3) the flowable composite resin leached more TEGDMA than the nano-hybrid.     

Shrinkage strain-rates of dental resin-monomer and composite systems

The purpose of this study was to investigate the shrinkage strain rate of different monomers, which are commonly used in dental composites and the effect of monomer functionality and molecular mass on the rate. Bis-GMA, TEGDMA, UDMA, MMA, HEMA, HPMA and different ratios of Bis-GMA/TEGDMA were mixed with Camphorquinone and Dimethyl aminoethyle methacrylate as initiator system. The shrinkage strain of the samples photopolymerised at Ca. 550 mW/cm2 and 23 degrees C was measured using the bonded-disk technique of Watts and Cash (Meas. Sci. Technol. 2 (1991) 788-794), and initial shrinkage-strain rates were obtained by numerical differentiation. Shrinkage-strain rates rose rapidly to a maximum, and then fell rapidly upon vitrification. Strain and initial strain rate were dependent upon monomer functionality, molecular mass and viscosity. Strain rates were correlated with Bis-GMA in Bis-GMA/TEGDMA mixtures up to 75-80 w/w%, due to the higher molecular mass of Bis-GMA affecting termination reactions, and then decreased due to its higher viscosity affecting propagation reactions. Monofunctional monomers exhibited lower rates. UDMA, a difunctional monomer of medium viscosity, showed the highest shrinkage strain rate (P < 0.05). Shrinkage strain rate, related to polymerization rate, is an important factor affecting the biomechanics and marginal integrity of composites cured in dental cavities. This study shows how this is related to monomer molecular structure and viscosity. The results are significant for the production, optimization and clinical application of dental composite restoratives.     

Evaluation of New Tri-methacrylates as a Reactive Diluent in Root Canal Sealant

In this work, a novel tri-methacrylate oligomer, GPTEMA, with three long-branched chain structures was synthesized through the reaction of glycerol propoxylate triglycidyl ether (GPTE) and methacrylic acid. The structure of GPTEMA was confirmed by FT-IR, ¹H-NMR, gel-permeation chromatography (GPC) and element analysis. The GPTEMA was used to partially or completely replace TEGDMA as reactive diluent and applied in a root canal sealant system containing Bis-GMA. The effects of GPTEMA on the polymerization behavior of Bis-GMA/TEGDMA/GPTEMA co-polymer and properties of its polymerizing product were investigated. Polymerization shrinkage, double bond conversion, glass transition temperature, flexural strength, flexural modulus, water sorption and diffusion coefficient of the Bis-GMA/TEGDMA/GPTEMA co-polymer were measured. The results illustrated that the Bis-GMA/TEGDMA/GPTEMA co-polymer attained lower polymerization shrinkage and higher double bond conversion. However, its T _g, flexural strength and flexural modulus decreased with increasing content of GPTEMA, water sorption and diffusion coefficient increased with increasing content of GPTEMA.     

Dental composites based on amorphous calcium phosphate - resin composition/physicochemical properties study

This study explores how the resin composition/structure affects the physicochemical properties of copolymers and their amorphous calcium phosphate (ACP)-filled composites. A series of photo-polymerizable binary and ternary matrices are formulated utilizing 2,2-bis[ p-(2(')-hydroxy-3(')methacryloxypropoxy)phenyl]propane, 2,2-bis[ p-(2(')-methacryloxypropoxy)phenyl]-propane (EBPADMA), or a urethane dimethacrylate as base monomers, and triethylene glycol dimethacrylate or hexamethylene dimethacrylate (HmDMA) with or without 2-hydroxyethyl methacrylate (HEMA) as diluent monomer. Unfilled copolymers and composites filled with 40% by mass zirconia-hybridized ACP are evaluated for biaxial flexure strength (BFS), degree of conversion (DC), mineral ion release, polymerization shrinkage (PS), and water sorption (WS). The average DC values are 82-94% and 74-91% for copolymers and composites, respectively. Unrelated to the resin composition, the PS values of composites are up to 8.4 vol. % and the BFS values of wet composite specimens are on average 51 +/- 8 MPa. The maximum WS values attained in copolymers and composites reach 4.8 mass%. Inclusion of hydrophobic HmDMA monomer in the matrices significantly reduces the WS. The levels of Ca and PO(4) released from all types of composites are significantly above the minimum necessary for the re-deposition of apatite to occur. Elevated Ca, and to a lesser extent PO(4) release, is observed in HEMA-containing, ternary EBPADMA formulations. Further resin reformulations may be needed to improve the PS of composite specimens. Poor dispersion of ;as-synthesized' ACP within the composite contributes to their inferior mechanical performance.     

Elution study of unreacted Bis-GMA, TEGDMA, UDMA, and Bis-EMA from light-cured dental resins and resin composites using HPLC

In the present work the elution of residual monomers from light-cured dental resins and resin composites into a 75% ethanol:water solution was studied using High-Performance Liquid Chromatography (HPLC). The resins studied were made by light-curing of bisphenol A glycol dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), ethoxylated bisphenol A glycol dimethacrylate [Bis-EMA(4)] and mixtures of these monomers. The resin composites were made from two commercial light-cured restorative materials (Z100 MP and Filtek Z250), the resin matrix of which is based on copolymers of these monomers. The effect of the curing time on the amount of monomers eluted was investigated. The concentration of the extractable monomers was determined at several immersion periods from 3 h to 30 days. For all the materials studied, it was observed that the chemical structure of the monomers used for the preparation of the resins, which defines the chemical and physical structure of the corresponding resin, directly affects the amount of eluted monomers, as well as the time needed for the elution of this amount. In the case of composites, it seems that the elution process it is not influenced by the presence of filler.